Image scanners are used in copiers, scanners, facsimiles and/or the like. The image scanner is a device for scanning an entire image by scanning the image in a scanning position using a one-dimensional imaging element, and is provided with a lighting unit for accomplishing lighting when reading an original. In the image scanner, it is necessary to scan the image information with good accuracy and at high speed, so a lighting unit composition has been disclosed for uniformly lighting the original with high efficiency. As general expressions, the direction in which a one-dimensional imaging element is arrayed is called the main scanning direction, and the direction of scanning is called the sub-scanning direction. In addition, the direction orthogonal to both the main scanning direction and the sub-scanning direction is called the focal depth direction in a scanning optical system and is called the lighting depth direction in a lighting unit.
The document lighting unit disclosed in Patent Literature 1 is provided with point light sources such as multiple LEDs (Light Emitting Diodes) arranged in the main scanning direction. The direction in which light is emitted from these point light sources is roughly parallel to the normal direction to the document stand on which a document is loaded and is in the opposite direction from the document stand. Light from these point light sources is guided to the document surface as lighting light by multiple reflective surfaces arranged facing the point light sources.
The condensing lighting device disclosed in Patent Literature 2 is provided with a light source positioned at the focal position of a reflective surface on a parabola, and a lens having two types of curvature for condensing light from the light source and light from the reflective surface.
The document lighting device disclosed in Patent Literature 3 is provided with LED elements disposed along the main scanning direction, and a reflective plate surrounding the LED elements. The shape of this reflective plate is a parabolic two-dimensional curve.
Patent Literature 4 discloses the composition of a light guide, lighting unit and image-scanning lighting device capable of realizing lighting with high illumination, large lighting depth and broad lighting width in the sub-scanning direction.